strlen optimization of decompose strcat?!

["Andreas Krebbel" <krebbel at linux dot vnet dot ibm dot com>]

Hi,

on s390 a strcat is already decomposed by fold_builtin_strcat into a
strlen and a strcpy.  Due to that 3 strlenopt testcases currently
fail: strlenopt-17g.c, strlenopt-4.c, strlenopt-4g.c.

For strlenopt-4.c no optimization is expected anyway (stpcpy
disabled). So this can easily be fixed by adding s390 specific scan
values.

The other two probably could be fixed by modifying the strlen
optimization to be able to reconstruct the strcat semantics.

The attached quick hack fixes strlenopt-17g.c for s390 without
regressions on x86_64.

For strlenopt-4g.c I only could get it working with setting (too) many
dont_invalidate flags on strinfos.  Otherwise the information needed
to reconstruct the strcat semantics don't survive long enough.

Perhaps we can remove the strcat folding relying on the strlen
optimization pass to catch all relevant cases?

Bye,

-Andreas-

Index: gcc/tree-ssa-strlen.c
===================================================================
*** gcc/tree-ssa-strlen.c.orig
--- gcc/tree-ssa-strlen.c
*************** get_string_length (strinfo si)
*** 397,403 ****
        callee = gimple_call_fndecl (stmt);
        gcc_assert (callee && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL);
        lhs = gimple_call_lhs (stmt);
!       gcc_assert (builtin_decl_implicit_p (BUILT_IN_STRCPY));
        /* unshare_strinfo is intentionally not called here.  The (delayed)
  	 transformation of strcpy or strcat into stpcpy is done at the place
  	 of the former strcpy/strcat call and so can affect all the strinfos
--- 397,403 ----
        callee = gimple_call_fndecl (stmt);
        gcc_assert (callee && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL);
        lhs = gimple_call_lhs (stmt);
!       gcc_assert (builtin_decl_implicit_p (BUILT_IN_STPCPY));
        /* unshare_strinfo is intentionally not called here.  The (delayed)
  	 transformation of strcpy or strcat into stpcpy is done at the place
  	 of the former strcpy/strcat call and so can affect all the strinfos
*************** handle_builtin_strcpy (enum built_in_fun
*** 1115,1127 ****
    dsi->writable = true;
    dsi->dont_invalidate = true;
  
!   if (dsi->length == NULL_TREE)
      {
        /* If string length of src is unknown, use delayed length
  	 computation.  If string lenth of dst will be needed, it
  	 can be computed by transforming this strcpy call into
  	 stpcpy and subtracting dst from the return value.  */
!       dsi->stmt = stmt;
        return;
      }
  
--- 1115,1144 ----
    dsi->writable = true;
    dsi->dont_invalidate = true;
  
!   if (builtin_decl_implicit_p (BUILT_IN_STPCPY) && dsi->length == NULL_TREE)
      {
+       strinfo psi;
+ 
        /* If string length of src is unknown, use delayed length
  	 computation.  If string lenth of dst will be needed, it
  	 can be computed by transforming this strcpy call into
  	 stpcpy and subtracting dst from the return value.  */
!       psi = get_strinfo (dsi->prev);
!       if (psi
! 	  && psi->next == dsi->idx
! 	  && psi->first == dsi->first
! 	  && psi->endptr == dsi->ptr)
! 	{
! 	  strinfo npsi = unshare_strinfo (psi);
! 	  npsi->stmt = stmt;
! 	  npsi->next = 0;
! 	  npsi->length = NULL_TREE;
! 	  npsi->endptr = NULL_TREE;
! 	  npsi->dont_invalidate = true;
! 	}
!       else
! 	dsi->stmt = stmt;
! 
        return;
      }